The invention relates to a tandem axle having two drivable axles, wherein each axle comprises a differential with a drive gearwheel, which can be driven by a shaft, as differential input, and two drive half-shafts, which drive the wheels on this axle by way of axle shaft gears.
DE 39 12 172 A1 discloses a vehicle four-wheel drive, the drive system of which comprises an engine, a manual shift transmission, two front wheels driven directly by said transmission and two selectively engageable rear wheels. A drivetrain comprising a prop shaft, a differential and two drive half-shafts is arranged between the rear wheels and the manual shift transmission. The rear wheels are each driven by way of a freewheel clutch, provided that when the prop shaft is engaged, the clutch arranged between the respective freewheel clutch and the drive half-shafts is closed.
The present invention provides a tandem axle equipped with two drivable axles, which will help to cut the fuel consumption of the vehicle and to reduce the tire wear on the axle.
This is achieved by a tandem axle having two drivable axles, each axle comprising a differential with a drive gear-wheel that can be driven by a shaft as a differential input and two drive half shafts that drive the wheels of this axle by way of axle shift gear. Here the wheels of the first axle are permanently and positively coupled to the drive gearwheel on this axle. The drive gearwheel on the first axle has a drive shaft on which a selectively engageable transfer gear is seated. The transfer gear meshes with a drive-through shaft gear, arranged rotationally locked on a drive-through shaft. The output of the drive-through shaft is coupled by way of intermediate members to the input-side drive gear wheel on the second axle. Shifting clutches are arranged in the second axle between the axle shaft gears and their adjacent wheels.
In conventional tandem axles the entire torque delivered by the drive is transmitted to the road surface via two axles, regardless of whether the torque is required or not. The full torque is often only needed when driving off or in uphill driving. Apart from the latter operating state it will generally suffice to transmit a reduced torque via just the first of the two axles, for example. In order to provide the full torque for these situations, an automated clutch, for example, may control or regulate the separation and restoration of the power flow between the first and the second axle.
Disconnecting an entire axle, as necessary, including the shutdown of the drivetrain between the first axle and the wheels of the second axle, affords a measurable saving in running costs. The trailing of the second axle serves to reduce the fuel consumption and the tire wear, together with the mechanical wear of all gearwheels and joints involved in driving this axle. There are furthermore no splash losses in the differential of the second axle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.